a) Field of the Invention
The present invention relates to a method of making wiring layer used for the manufacture of integrated circuits such as LSIs, and more particularly to a method of making a wiring layer capable of improving an anticorrosion function and easily removing a resist film during a resist ashing process after patterning a wiring layer.
b) Description of the Related Art
A conventional method of making wiring layer for LSIs or the like such as shown in FIG. 7 is known. An aluminum (Al) based wiring material layer, i.e. Al or Al alloy is deposited on an insulting film 12 such as silicon oxide covering the surface of a semiconductor substrate 10 such as silicon. Thereafter, a resist layer 16 is formed thereon and patterned in a desired layout. Using the resist layer 16 as a mask, the Al based wiring material layer is selectively etched by using a Cl based gas such as BCl.sub.3 and Cl.sub.2 to form a wiring layer 14.
Thereafter, an ashing process is performed to remove the resist layer 16 and by-products generated during the etching process. The ashing process is defined as a process which resolves a resist and by-products during etching process to thereby remove them from a semiconductor substrate. The ashing process is performed under plasma assisted circumstances, and the reaction mechanism of the plasma-assisted ashing process including oxygen is considered as follows: EQU C.sub.x H.sub.y +{2x+(y/2)}O(radical).increment.xCO.sub.2 .uparw.+(y/2)H.sub.2 O
i.e., oxygen radical generated in the plasma reacts with organic materials included in the resist materials, the resist materials are oxidized and resolved. The ashing process has been performed heretofore by two methods. The first method performs the ashing by using a plasma of a mixed gas of a fluorine (F) containing gas such as CF.sub.4 and an O.sub.2 gas. The second method performs the ashing by using a plasma of a mixed gas, which contains hydrogen and oxygen (a H-and-O containing gas) such as CH.sub.3 OH (methyl alcohol) and an O.sub.2 gas. Reference may be made to Japanese Patent Laid-open Publications Nos. 58-87276 and 3-83337 respectively for the first and second methods.
The first method cannot remove Cl components sufficiently, which have attached during the etching process on the surface of the wafer. The unremoved Cl components may corrode a wiring. For a laminated layer having a barrier metal layer such as TiW and TiN under the Al based wiring material layer, there are not only the unremoved Cl components but also local batteries formed by the layers. Thus, corrosion can more likely occur.
The second method is an improved version of the first method. With the second method, however, it is necessary to heat a substrate or wafer to about 200.degree. to 350.degree. C. order to obtain a practical ashing speed. This heating process alters the quality of, and cures, the resist surface layer in which the etching gas and by-products (such as AlCl.sub.x, CuCl.sub.2, SiCl.sub.x) have been mixed. As shown in FIG. 7, resist surface layers of the resist film 16, particularly resist surface layers 16a and 16b, may be left unremoved which are in some cases called rabbit ears.
Although such resist surface layers 16a and 16b may also be left unremoved when using the first method, these layers can be readily washed out by amine based solvent. However, with the second method, the quality change and curing of the resist surface layer reached sometimes to the extent that the surface layer cannot be removed even if it is processed by amine based solvent, lowering the manufacturing yield.
It has been tried to lower the heating temperature avoid the quality change and curing of a resist film. However, with a lowered temperature, not only the ashing speed lowers but also the anticorrosion function deteriorates.